1. Field of the Invention
The present invention relates generally to an optical signal coupling block, and a multi-layer printed circuit board and method for coupling optical signals between layers of the multi-layer printed circuit board using the same, and more particularly to a method for coupling optical signals between layers of a multi-layer printed circuit board by optically interconnecting optical waveguides to optical fibers using fiber or pipe blocks having grooves of certain shapes where plastic optical fibers are inserted.
2. Description of the Prior Art
Generally, a Printed Circuit Board (PCB) is a circuit board fabricated by densely mounting a plurality of components on a plate made of phenol resin or epoxy resin and densely forming curtailed circuits on the surface of the plate to connect the respective components to each other. Such a PCB is manufactured by placing a conductive film, such as a copper film, on one surface of a phenol or epoxy resin insulation plate, forming circuit patterns through (whereby the copper film is then corroded away except for the line-shaped circuits), and forming holes to allow electrical components to be mounted on the insulating plate.
PCBs are classified into single-sided PCBs, double-sided PCBs and multi-layer PCBs according to the number of circuit pattern surfaces. As the number of layers of a PCB increases, the capacity to mount components thereon increases greatly, so PCBs having many layers are applied to high precision products. A multi-layer PCB designates a PCB having three or more layers including a surface conductive pattern. The conductive patterns are formed on the respective layers of the PCB while being separated from each other by insulation materials provided between the respective layers.
On the other hand, in the prior art, circuit patterns are formed on a copper plate (through a patterning process) at the time of manufacturing a PCB to form inner and outer layers of the PCB. Recently, one or more optical waveguides capable of transmitting and receiving signals via light through the use of polymer materials and glass fibers are inserted into a PCB, which is called an Electro-Optical Circuit Board (EOCB). Such an EOCB is a PCB in which one or more optical waveguides and one or more glass plates are inserted into a base board on which copper circuit patterns are formed; so electrical and optical signals are used together, thus performing super-high speed data communication in the same board through optical signal interfacing, and converting the optical signals into electrical signals in each mounted device so as to store data and process signals.
Currently, several coupling methods have been proposed for coupling optical signals between respective layers of a multi-layer PCB. Generally, a direct writing method, a beam reflection method, a method using a reflection mirror, and a direct coupling method are employed as methods of coupling optical signals between multi-channel layers.
Hereinafter, an example of an optical interface in a conventional PCB is described with reference to FIG. 1.
FIG. 1 shows a conventional beam coupling technology using a beam reflecting micro mirror.
Referring to FIG. 1, if an electrical signal is input from a processor board 2, the electrical signal is converted into an optical signal by a laser diode 1 in a transmission module 3 mounted on a PCB, and the optical signal is radiated. Thereafter, the radiated optical signal passes through lenses 8a and 8b on the left side of FIG. 1 and is reflected by a micro mirror 4a inserted into the PCB and depicted on the right side of FIG. 1. The reflected optical signal passes through an optical waveguide and is then reflected by a reflection mirror 4b on the right side of FIG. 1. Thereafter, the reflected optical signal is transmitted to a photodiode 6 in a reception module 7 through lenses 8c and 8d on the left side of FIG. 1. In the optical waveguide, the optical signal is transferred through its multi-mode polymer cores 5a and 5b with low loss. A waveguide cladding 9 is formed above and under the cores 5a and 5b. Consequently, an electrical signal transmitted from the processor board 2 on the left side of FIG. 1 is converted into an optical signal and transmitted. Thereafter, the optical signal is again converted into an electrical signal and then transmitted to a processor board on the left side of FIG. 1.
A conventional multi-layer PCB for coupling optical signals is described with reference to FIGS. 2a and 2b. 
FIGS. 2a and 2b are front and side sectional views of the conventional multi-layer PCB for coupling optical signals, respectively. Referring to FIGS. 2a and 2b, the conventional multi-layer PCB employs a manner in which, if light is emitted from each Vertical-Cavity Surface-Emitting Laser (VCSEL) 13, that is, a light source device, a micro lens 17 concentrates the light and transmits the concentrated light to an optical waveguide 14 and 15 through PCB optical via holes 16. At this time, signal coupling between respective layers is performed in the same manner as described above. In this case, a Silicon Optical Bench (SiOB) 12 is formed on a PCB 11, wherein the SiOB is a term generally designating silicon wafers. Instead of the SiOB 12, a polymer board can be used. The optical waveguide typically includes a cladding 14 and a core 15, and functions to transfer light received from the VCSEL 13 through the micro lens 17. Thereafter, an optical signal 19 is transferred to an optical waveguide of another layer. In this case, each of the optical via holes 16 is insulated with an insulation material 18. Further, a micro lens 17′ can be inserted into each of the optical via holes 16 so as to more reliably transmit the optical signal.
The VCSEL 13 designates a light source used in an optical module that transmits and amplifies optical source data using a manner in which circular laser beams are emitted perpendicularly to the surface of a board. So far Light Emitting Diodes (LEDs) and edge emitting Laser Diodes (LDs) have been generally used. However, Surface-Emitting Lasers (SELs) developed in the 1990s have been gaining popularity as light sources, replacing LEDs and edge emitting LDs. Such VCSELs are used in optical fiber communications, interfacing, large capacity information parallel processing, etc.
However, the conventional multi-layer PCB using the optical via holes 16 to transmit the optical signal 19 is problematic in that the micro lens 17 must be used, and the wavelength of an optical signal that can be transmitted through the conventional multi-layer PCB is limited to 200 μm.
Further, in the prior art, many coupling methods for waveguides using curved surface reflection mirrors or prisms have been proposed. However, theses coupling methods are problematic in that it is difficult to insert reflection mirrors or prisms into base boards and attach the mirrors or prisms to the base boards, and alignment errors may occur between the reflection mirrors or prisms and the base boards when respective layers are processed in a single line using several mechanical drills to couple multi-channel signals in cases where a multi-layer PCB is manufactured.